The present invention relates to a method of producing a semiconductor device, particularly one having a buffer coat layer and sealed in a mold resin.
A semiconductor device or chip having a passivation film on its surface and sealed in a mold resin is conventional. Recently, the increasing size of this type of semiconductor device has brought about a problem that a gap is formed at the interface between the passivation film and the mold resin due to a heavy stress acting therebetween, thereby deteriorating the moisture proof feature of the device, among others. To reduce stress, there has been proposed a semiconductor device having a polyimide film or buffer layer between the mold resin and the passivation film.
To produce semiconductor device chips, it is necessary that the passivation film and polyimide film be formed with openings in their portions corresponding to scribe lines and bonding pads and be separated therealong. This can be done if each of the passivation film and polyimide films is patterned through a respective mask implemented by may photoresist. Alternatively, the polyimide film may be patterned first, and then the passivation film may be patterned through the patterned polyimide film. The former method, however, needs a great number of steps which increase manufacturing time. The latter method is disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 4-025047 and 4-043641. However, the problem with this method, i.e., patterning the passivation film with the hardened polyimide film serving as a mask is that the ions of fluorine-based gas used to etch the passivation film remain on the surface of the polyimide film. The ions cause the exposed portions of Al (aluminum)-based metal to corrode due to moisture in the air. To reduce the corrosion, i.e., to remove the fluorine ions, there has been proposed a method which ashes the surface of the polyimide film by oxygen and then removes only a part of the surface by etching back. This, however, brings about another problem that oxygen for ashing dissociates the imide coupling of the polyimide surface and thereby lowers the adhesion of the polyimide to the mold resin.